Ion generator and ion implanter

ABSTRACT

An ion generator includes an arc chamber defining a plasma generation space, and a cathode which emits thermoelectrons toward the plasma generation space. The arc chamber includes a box-shaped main body having an opening, and a slit member mounted to cover the opening and provided with a front slit. An inner surface of the main body is exposed to the plasma generation space made of a refractory metal material. The slit member includes an inner member made of graphite and an outer member made of another refractory metal material. The outer member includes an outer surface exposed to an outside of the arc chamber. The inner member includes an inner surface exposed to the plasma generation space, and an opening portion which forms the front slit extending from the inner surface of the inner member to the outer surface of the outer member.

RELATED APPLICATIONS

This is a continuation of application Ser. No. 16/818,675 filed on Mar.13, 2020, the contents of which, including the specification, the claimsand the drawings, are incorporated herein by reference in theirentirety. The contents of Japanese Patent Application No. 2019-049842,on the basis of which priority benefits are claimed in an accompanyingapplication data sheet, including the claims, the specification and thedrawings, are incorporated herein by reference in their entirety.

BACKGROUND Technical Field

Certain embodiments of the present invention relate to an ion generatorand an ion implanter.

Description of Related Art

In a semiconductor manufacturing process, for the purpose of changingthe conductivity of a semiconductor, the purpose of changing the crystalstructure of the semiconductor, or the like, a process of implantingions into a semiconductor wafer is carried out standardly. An apparatuswhich is used in this process is generally called an ion implanter. Insuch an ion implanter, ions are generated by an ion generator providedwith an indirectly heated cathode structure and an arc chamber. Thegenerated ions are extracted to the outside of the arc chamber throughan extraction electrode.

SUMMARY

According to an embodiment of the present invention, there is providedan ion generator including: an arc chamber which defines a plasmageneration space; a cathode which emits thermoelectrons toward theplasma generation space; and a repeller which faces the cathode with theplasma generation space interposed therebetween, wherein the arc chamberincludes a box-shaped main body in which a front side is open, and aslit member which is mounted to the front side of the main body andprovided with a front slit for extracting ions, an inner surface of themain body which is exposed to the plasma generation space is made of arefractory metal material, and an inner surface of the slit member whichis exposed to the plasma generation space is made of graphite.

According to another embodiment of the present invention, there isprovided an ion implanter including: the ion generator according to theabove embodiment; a beam acceleration unit that accelerates an ion beamwhich is extracted from the ion generator to have an energy of 1 MeV orhigher; and an implantation process chamber in which a wafer isirradiated with an ion beam which exits from the beam acceleration unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view showing a schematic configuration of an ionimplanter according to an embodiment.

FIG. 2 is a sectional view showing a schematic configuration of an iongenerator according to the embodiment.

FIG. 3 is a plan view showing a schematic configuration of an outersurface side of a slit member.

FIG. 4 is a plan view showing a schematic configuration of an innersurface side of the slit member.

FIG. 5 is a sectional view showing a schematic configuration of an arcchamber.

FIG. 6 is a sectional view showing the schematic configuration of thearc chamber.

FIG. 7 is a sectional view showing the schematic configuration of thearc chamber.

FIG. 8 is a side view schematically showing a method of fixing the slitmember.

FIG. 9 is a side view schematically showing the method of fixing theslit member.

DETAILED DESCRIPTION

In recent years, there is a case where it is required to generate ahigh-energy ion beam in order to implant ions into a deeper region of awafer surface. In order to generate the high-energy ion beam, it isnecessary to generate multiply charged ions in an ion generator andaccelerate the multiply charged ions by using a direct-currentacceleration mechanism or a radio frequency acceleration mechanism (forexample, a linear acceleration mechanism). In a case of generating asufficient amount of multiply charged ions in the ion generator, it isnecessary to increase an arc voltage or an arc current, and thus wear ofan arc chamber or an electric discharge between the arc chamber and anextraction electrode can become more prominent. Under such a condition,mixing of contamination due to the wear of the arc chamber, damage to anapparatus due to the electric discharge, or the like can becomeproblematic.

It is desirable to provide an ion generator in which it is possible tosuppress mixing of contamination and damage due to an electric dischargeunder a condition that generate more multiply charged ions.

Any combination of the constituent elements described above, orreplacement of constituent elements or expressions of the presentinvention with each other between methods, apparatuses, systems, or thelike is also valid as an aspect of the present invention.

According to the present invention, an ion generator capable of stablygenerating high-purity multiply charged ions can be provided.

Hereinafter, modes for carrying out the present invention will bedescribed in detail with reference to the drawings. In the descriptionsof the drawings, the same elements are denoted by the same referencenumerals, and overlapping descriptions are omitted appropriately.Further, the configuration described below is an exemplification anddoes not limit the scope of the present invention.

FIG. 1 is a top view showing a schematic configuration of an ionimplanter 100 according to an embodiment. The ion implanter 100 is aso-called high-energy ion implanter. The ion implanter 100 extracts andaccelerates ions generated in an ion generator 10 to generate an ionbeam IB, transports the ion beam IB to an object to be processed (forexample, a substrate or a wafer W) along a beamline, and implants theions into the object to be processed.

The ion implanter 100 includes a beam generation unit 12 that generatesand mass-separates ions, a beam acceleration unit 14 that furtheraccelerates the ion beam IB to obtain a high-energy ion beam, a beamdeflection unit 16 that performs energy analysis, energy dispersioncontrol, trajectory correction of the high-energy ion beam, and a beamtransport unit 18 that transports the analyzed high-energy ion beam tothe wafer W, and a substrate transferring/processing unit 20 in that thetransported high-energy ion beam is implanted into a semiconductorwafer.

The beam generation unit 12 includes the ion generator 10, an extractionelectrode 11, and a mass analyzer 22. In the beam generation unit 12,ions are extracted from the ion generator 10 through the extractionelectrode 11 and accelerated at the same time, and the extracted andaccelerated ion beam is subjected to mass analysis by the mass analyzer22. The mass analyzer 22 includes a mass analyzing magnet 22 a and amass resolving aperture 22 b. As a result of the mass analysis by themass analyzer 22, ion species necessary for implantation are selected,and an ion beam of the selected ion species is led to the following beamacceleration unit 14.

The beam acceleration unit 14 includes a plurality of linearaccelerators that accelerate the ion beam, that is, one or more radiofrequency resonators. The beam acceleration unit 14 is a radio frequencyacceleration mechanism that accelerates ions by the action of a radiofrequency (RF) electric field. The beam acceleration unit 14 includes afirst linear accelerator 15 a which is provided with standardmultiple-stage radio frequency resonators, and a second linearaccelerator 15 b which is provided with additional multiple-stage radiofrequency resonators for high-energy ion implantation. The direction ofthe ion beam accelerated by the beam acceleration unit 14 is changed bythe beam deflection unit 16.

The high-energy ion beam which exits from the beam acceleration unit 14has a certain range of energy distribution. For this reason, in order toirradiate the wafer with the high-energy ion beam that is reciprocallyscanned and parallelized downstream of the beam acceleration unit 14, itis necessary to carry out high-accuracy energy analysis, trajectorycorrection, and adjustment of beam convergence and divergence inadvance.

The beam deflection unit 16 performs the energy analysis, energydispersion control, and trajectory correction of the high-energy ionbeam. The beam deflection unit 16 includes at least two high-accuracybending electromagnets, at least one energy width limiting slit, atleast one energy resolving aperture, and at least one laterally focusingdevice. The plurality of bending electromagnets are configured toperform the energy analysis of the high-energy ion beam and accuratecorrection of an ion implantation angle.

The beam deflection unit 16 includes an energy analyzing electromagnet24, a laterally focusing quadrupole lens 26 that suppresses energydispersion, an energy resolving aperture 28, and a bending electromagnet30 that provides beam steering (ion beam trajectory correction). Theenergy analyzing electromagnet 24 is sometimes referred to as an energyfilter electromagnet (EFM). The high-energy ion beam is subjected to adirection change by the beam deflection unit 16 to travel toward thewafer W.

The beam transport unit 18 is a beamline unit that transports the ionbeam IB exited from the beam deflection unit 16, and includes a beamshaper 32 composed of a focusing/defocusing lens group, a beam scanner34, a beam parallelizer 36, and a final energy filter 38 (including afinal energy separation slit). The length of the beam transport unit 18is designed in accordance with the total length of the beam generationunit 12 and the beam acceleration unit 14, and the beam transport unit18 is connected to the beam acceleration unit 14 with the beamdeflection unit 16 to form a U-shaped layout as a whole.

The substrate transferring/processing unit 20 is provided at theterminus on the downstream side of the beam transport unit 18. Thesubstrate transferring/processing unit 20 includes an implantationprocess chamber 42 and a substrate transfer unit 44. The implantationprocess chamber 42 is provided with a platen driving device 40 thatholds the wafer W which is being subjected to ion implantation, andmoves the wafer W in a direction perpendicular to a beam scanningdirection. The substrate transfer unit 44 is provided with a wafertransfer mechanism such as a transfer robot for loading the wafer Wbefore the ion implantation into the implantation process chamber 42 andunloading the ion-implanted wafer W from the implantation processchamber 42.

The ion generator 10 is configured to generate, for example, multiplycharged ions of boron (B), phosphorus (P), or arsenic (As). The beamacceleration unit 14 accelerates the multiply charged ions extractedfrom the ion generator 10 and generates a high-energy ion beam of 1 MeVor higher or 4 MeV or higher. By accelerating the multiply charged ions(for example, doubly charged ions, triply charged ions, quadruplycharged ions or higher), a high-energy ion beam can be generated moreefficiently than in a case of accelerating singly charged ions.

The beam acceleration unit 14 may not be a two-stage linear acceleratoras illustrated, and may be configured as a single linear accelerator asa whole, or may be configured to be divided into three or more stages oflinear accelerators. Further, the beam acceleration unit 14 may beconfigured with any other type of acceleration unit, and may be providedwith a direct-current acceleration mechanism, for example. Thisembodiment is not limited to a specific ion acceleration method, and anybeam acceleration unit can be adopted as long as it can generate ahigh-energy ion beam of 1 MeV or higher or 4 MeV or higher.

According to the high-energy ion implantation, since desired impurityions are implanted into the wafer surface with a higher energy than inthe ion implantation of an energy of less than 1 MeV, it is possible toimplant desired impurities into a deeper region (for example, a depth of5 μm or more) on the wafer surface. The high-energy ion implantation isused for, for example, the formation of P-type regions and/or N-typeregions in the manufacture of semiconductor devices such as the newestimage sensors.

The ion generator 10 according to this embodiment is a type using aso-called indirectly heated cathode (IHC) and generates arc discharge inan arc chamber to generate multiply charged ions. In order to generatemultiply charged ions, it is necessary to increase an arc voltage or anarc current in order to strip more electrons from atoms. Under such anarc condition, wear of the interior of the arc chamber becomes severe,and there is a high possibility that a part of a member configuring theinner wall of the arc chamber may also be ionized and extracted to theoutside of the arc chamber. As a result, the ion beam IB in which theconstituent members of the arc chamber are mixed as contaminants isimplanted into the wafer W, and thus there is a concern that thecharacteristics of a semiconductor device which is formed on the wafer Wmay be affected.

Further, under the condition that the arc voltage or the arc current islarge, the amount of ions which are extracted from the arc chamberincreases and an electric discharge easily occurs between the arcchamber and the extraction electrode. Depending on aspect of occurrenceof the electric discharge, there is a concern that the arc chamber maybe damaged, and in a case where the electric discharge or the damageoccurs frequently, the life of the arc chamber is shortened, so thatfrequent maintenance of the apparatus is required. In that case, theoperation rate of the ion implanter 100 is lowered and the productionefficiency of a semiconductor device is lowered.

Therefore, in this embodiment, an ion generator is provided which cansuppress mixing of contamination into the ion beam or damage to the arcchamber due to an electric discharge, even in a case of generating moremultiply charged ions. In order to prevent mixing of contamination intothe ion beam, it is important to increase the purity of the memberconfiguring the arc chamber, and from the viewpoint of suppressingcontamination, high-purity and refractory graphite is suitable. On theother hand, graphite is a material that is easily worn by plasma whichis generated in the arc chamber, and carbon compounds which aregenerated by a reaction with the plasma are deposited on the surfaces ofthe constituent members of the ion generator, thereby causing dirt.Further, in use of graphite, an electric discharge more easily occursthan in use of a refractory metal material, and graphite is easilydamaged when the electric discharge occurs. Therefore, in thisembodiment, an ion generator capable of suppressing mixing ofcontamination and damage due to an electric discharge is provided byappropriately combining graphite and a refractory metal material, basedon a difference in material characteristic.

FIG. 2 is a diagram showing a schematic configuration of the iongenerator 10 according to the embodiment. The ion generator 10 is anindirectly heated ion source, and includes an arc chamber 50, a cathode56, a repeller 58, and various power sources.

The extraction electrode 11 for extracting the ion beam IB through afront slit 60 of the arc chamber 50 is disposed in the vicinity of theion generator 10. The extraction electrode 11 includes a suppressionelectrode 66 and a ground electrode 68. A suppression power source 64 fis connected to the suppression electrode 66, and a negative suppressionvoltage is applied to the suppression electrode 66. The ground electrode68 is connected to ground 64 g.

The arc chamber 50 has a substantially rectangular parallelepiped boxshape. The arc chamber 50 defines a plasma generation space S in whichplasma is generated. In the drawing, a plasma forming region P in whichhigh-concentration plasma is formed is schematically shown by a brokenline. The arc chamber 50 includes a box-shaped main body 52 on which afront side 52 g is open, and a slit member 54 which is mounted to thefront side 52 g of the main body 52. The slit member 54 is provided withthe front slit 60 for extracting the ion beam IB. The front slit 60 hasan elongated shape extending in a direction (also referred to as anaxial direction) from the cathode 56 toward the repeller 58. Anextraction voltage which is positive with respect to the ground 64 g isapplied to the arc chamber 50 by an extraction power source 64 d.

The main body 52 has a back wall 52 b and four side walls including afirst side wall 52 c and a second side wall 52 d. The back wall 52 b isprovided at a position facing the front slit 60 with the plasmageneration space S interposed therebetween, and is disposed so as toextend in the axial direction. The back wall 52 b is provided with a gasintroduction port 62 for introducing a source gas. The four side wallsincluding the first side wall 52 c and the second side wall 52 d areprovided so as to define a rectangular opening of the front side 52 g ofthe main body 52. The first side wall 52 c and the second side wall 52 dare disposed to face each other in the axial direction. The first sidewall 52 c has a cathode insertion port 52 e extending in the axialdirection, and the cathode 56 is disposed in the cathode insertion port52 e. The second side wall 52 d has a repeller insertion port 52 fextending in the axial direction, and the repeller 58 is disposed in therepeller insertion port 52 f.

The main body 52 has an inner surface 52 a exposed to the plasmageneration space S and made of a refractory metal material, and forexample, refractory metal such as tungsten (W), molybdenum (Mo), ortantalum (Ta), or an alloy thereof is used. The entirety of the mainbody 52 may be made of a refractory metal material, or only the innersurface 52 a of the main body 52 may be selectively made of a refractorymetal material. The main body 52 can be made of tungsten having a highmelting point (about 3400° C.), for example. The purity of therefractory metal material which is used for the main body 52 may be astandard purity lower than that of other members (for example, thecathode 56 described later), and for example, the content rate of therefractory metal element is less than 99.99% by weight. An example ofthe refractory metal element content rate of the material which is usedfor the main body 52 is less than 99.8% by weight, less than 99.9% byweight, or less than 99.95% by weight.

The slit member 54 is a plate-shaped member in which the front slit 60is provided. The slit member 54 is mounted to the front side 52 g of themain body 52 so as to close the opening of the front side 52 g. The slitmember 54 has an inner surface 54 a which is exposed to the plasmageneration space S and is made of graphite, and an outer surface 54 bwhich is exposed to the outside of the arc chamber 50 is made of arefractory metal material. The slit member 54 has a double structurewhich includes an inner member 70 made of graphite and an outer member80 made of a refractory metal material, and in which the inner member 70and the outer member 80 overlap each other. The outer member 80 can bemade of a refractory metal material having a standard purity, similar tothe main body 52, and is made of tungsten, for example.

The inner member 70 has the inner surface 54 a which is exposed to theplasma generation space S. The inner member 70 has an inner opening 72for forming the front slit 60, and has a protrusion portion 74 whichprotrudes toward the outside of the arc chamber 50 in the vicinity or onthe periphery of the inner opening 72. The position of the outer surface74 b of the protrusion portion 74 in the thickness direction (thedirection from the inside toward the outside of the arc chamber 50)coincides with the position of the outer surface 54 b of the slit member54 (or the outer member 80) in the thickness direction. A slit recessportion 76 is formed inside of the protrusion portion 74, and the innersurface 54 a of the inner opening 72 is separated from the plasmaforming region P in the vicinity of the inner opening 72. The innermember 70 has a tapered surface 72 a provided at the edge of the inneropening 72 such that an opening size increases from the inside towardthe outside of the arc chamber 50. The edge of the inner opening 72 isformed in a tapered shape, whereby the front slit 60 that hardly hindersthe flow of the ion beam IB which is extracted from the inside towardthe outside of the arc chamber 50 can be formed.

The outer member 80 has an outer surface 54 b which is exposed to theoutside of the arc chamber 50, and is provided so as to face theextraction electrode 11 (the suppression electrode 66). The outer member80 is a cover that covers the outside of the inner member 70, and has arole of supporting the inner member 70 made of graphite having a lowmechanical strength to increase the strength. The outer member 80 has anouter opening 82 for forming the front slit 60. The opening size of theouter opening 82 is larger than the opening size of the inner opening72. The opening size of the outer opening 82 is larger than the size ofan outer periphery 74 a of the protrusion portion 74. The opening sizeof the outer opening 82 may be substantially the same as the size of theouter periphery 74 a of the protrusion portion 74, and for example, theouter opening 82 is configured such that the edge of the outer opening82 is provided along the outer periphery 74 a of the protrusion portion74.

The outer member 80 is preferably configured so as not to hinder theextraction of the ion beam IB which passes through the inner opening 72.Specifically, it is preferable that the outer member 80 is configuredsuch that the edge of the outer opening 82 is located at a positionfarther from a center 60 c of the front slit 60 than a virtual plane 72b obtained by extending the tapered surface 72 a of the inner opening 72toward the outside of the arc chamber 50. As a result, the opening shapeof the front slit 60 can be defined by only the inner opening 72, andthe outer member 80 can be prevented from being exposed to the ion beamIB which is extracted from the arc chamber 50.

The cathode 56 emits thermoelectrons toward the plasma generation spaceS. The cathode 56 is inserted into the cathode insertion port 52 e andfixed in a state where it is electrically insulated from the arc chamber50. The cathode 56 includes a filament 56 a, a cathode head 56 b, athermal break 56 c, and a thermal reflector 56 d.

The cathode head 56 b is a solid columnar member, and the tip thereof isexposed to the plasma generation space S. The thermal break 56 c is acylindrical member that supports the cathode head 56 b, and extends inthe axial direction from the outside toward the inside of the arcchamber 50. The thermal break 56 c desirably has a shape with highthermal insulation properties in order to maintain a high temperaturestate of the cathode head 56 b, and has a thin shape. The thermalreflector 56 d is a cylindrical member which is provided so as tosurround the outer peripheries of the cathode head 56 b and the thermalbreak 56 c. The thermal reflector 56 d reflects the radiant heat fromthe cathode head 56 b and the thermal break 56 c which are in a hightemperature state, so that the high temperatures of the cathode head 56b and the thermal break 56 c are maintained. The filament 56 a isdisposed so as to face the cathode head 56 b in the interior of thethermal break 56 c.

The filament 56 a is heated by a filament power source 64 a andgenerates thermoelectrons at the tip thereof. Primary thermoelectronsgenerated on the filament 56 a are accelerated by a cathode voltage (forexample, in a range of 300 to 600 V) of a cathode power source 64 b,collide with the cathode head 56 b, and heat the cathode head 56 b withthe energy which is generated due to the collision. The heated cathodehead 56 b generates secondary thermoelectrons, and the secondarythermoelectrons are accelerated by an arc voltage (for example, in arange of 70 to 150 V) applied between the cathode head 56 b and the arcchamber 50 by an arc power source 64 c. The accelerated secondarythermoelectrons are emitted toward the plasma generation space S as beamelectrons having sufficient energy in order to ionize the source gaswhich is introduced from the gas introduction port 62 and generateplasma containing multiply charged ions. The beam electrons which areemitted toward the plasma generation space S are restrained by amagnetic field B which is applied to the plasma generation space S inthe axial direction, and move spirally along the magnetic field B. Bycausing the electrons to move spirally in the plasma generation space S,it is possible to limit the movement of the electrons to the plasmaforming region P and increase the plasma generation efficiency.

The cathode head 56 b is made of a refractory metal material, forexample, tungsten. The cathode head 56 b may be made of a refractorymetal material having purity higher than standard purity, and may havethe refractory metal element content rate of 99.99% or more by weight.An example of the refractory metal element content rate of the materialwhich is used for the cathode head 56 b is 99.995% or more by weight,99.9995% or more by weight, or 99.9999% or more by weight. The cathodehead 56 b is a member that is easily worn out by being exposed tohigh-concentration plasma, and is a member that easily causes mixing ofcontamination into the ion beam IB. By increasing the purity of therefractory metal material configuring the cathode head 56 b, it ispossible to reduce the influence of the mixing of contamination into theion beam IB due to the ionization of the material configuring thecathode head 56 b. At least one of the thermal break 56 c and thethermal reflector 56 d may be made of a refractory metal material havingstandard purity, or may be made of a refractory metal material havinghigh purity, similar to the cathode head 56 b.

The repeller 58 repels the electrons in the arc chamber 50 and causesthe electrons to stay in the plasma forming region P to increase plasmageneration efficiency. The repeller 58 is inserted into the repellerinsertion port 52 f and is fixed in a state of being electricallyinsulated from the arc chamber 50. A configuration is made such that arepeller voltage (for example, in a range of 120 to 200 V) is appliedbetween the repeller 58 and the arc chamber 50 by a repeller powersource 64 e and electrons are repelled toward the plasma forming regionP.

The repeller 58 includes a repeller head 58 a, a repeller shaft 58 b,and a repeller support part 58 c. The repeller head 58 a is providedinside of the arc chamber 50 and is provided at a position facing thecathode head 56 b in the axial direction with the plasma generationspace S interposed therebetween. The repeller support part 58 c isprovided outside of the arc chamber 50 and is fixed to a supportstructure (not shown). The repeller shaft 58 b is a columnar memberwhich is inserted into the repeller insertion port 52 f, and connectsthe repeller head 58 a and the repeller support part 58 c. For example,female screws are formed in the repeller shaft 58 b, male screws areformed on the repeller head 58 a and the repeller support part 58 c, andthe repeller head 58 a, the repeller shaft 58 b, and the repellersupport part 58 c are connected to each other by a screw structure.

The repeller head 58 a is made of a refractory metal material, forexample, tungsten. The repeller head 58 a may be made of a refractorymetal material having high purity, similar to the cathode head 56 b. Therepeller head 58 a is a member that is easily worn out by being exposedto high-concentration plasma, similar to the cathode head 56 b, andthus, by increasing the purity of the material configuring the repellerhead 58 a, the influence of mixing of contamination into the ion beam IBcan be reduced. In a case where the repeller head 58 a is made of arefractory metal material, it is preferable that the repeller shaft 58 bis made of graphite. In this way, the seizure of the repeller head 58 aand the repeller shaft 58 b which are connected to each other by thescrew structure can be prevented. The repeller head 58 a may be made ofgraphite.

FIG. 3 is a plan view showing a schematic configuration of the side ofthe outer surface 54 b of the slit member 54 and shows a front view whenthe front slit 60 is viewed from the extraction electrode 11. The crosssection taken along the line A-A in FIG. 3 corresponds to FIG. 2. Theouter member 80 has a substantially rectangular external shape that islong in the axial direction. Further, the inner member 70 indicated by abroken line also has a substantially rectangular external shape that islong in the axial direction. The front slit 60 is provided at the centerof the slit member 54, and an opening shape thereof is defined by thesubstantially rectangular inner opening 72 which is elongated in theaxial direction. The outer periphery 74 a of the protrusion portion 74is also substantially rectangular, and the edge of the outer opening 82is also substantially rectangular. The outer member 80 is configured tocompletely cover the inner member 70 except for the protrusion portion74 in the vicinity of or around the front slit 60. Therefore, theexternal size of the outer member 80 is larger than the external size ofthe inner member 70 indicated by a broken line. Outer engagementportions 86 a, 86 b, 86 c, and 86 d for fixing the outer member 80 areprovided at four locations on the outer periphery of the outer member80. The outer engagement portions 86 a to 86 d are provided by two alongeach of two long sides of the outer periphery of the outer member 80.

FIG. 4 is a plan view showing a schematic configuration of the side ofthe inner surface 54 a of the slit member 54 and shows a rear view whenthe front slit 60 is viewed from the plasma generation space S. Thecross section taken along the line A-A in FIG. 4 corresponds to FIG. 2.A cathode accommodation recess portion 78 a, a repeller accommodationrecess portion 78 b, and a central recess portion 78 c are provided onthe inner surface 54 a of the inner member 70. The cathode accommodationrecess portion 78 a is provided at a position facing the cathode 56, andthe repeller accommodation recess portion 78 b is provided at a positionfacing the repeller 58. The central recess portion 78 c extends in theaxial direction along the front slit 60 and is provided so as to connectthe cathode accommodation recess portion 78 a and the repelleraccommodation recess portion 78 b. Each of the cathode accommodationrecess portion 78 a and the repeller accommodation recess portion 78 bis configured such that the inner surface thereof facing each of thecathode 56 and the repeller 58 is a flat surface or a cylindricallycurved surface. The central recess portion 78 c is configured such thatthe inner surface thereof which is exposed to the plasma generationspace S is a substantially cylindrically curved surface. The cathodeaccommodation recess portion 78 a, the repeller accommodation recessportion 78 b, and the central recess portion 78 c are provided, wherebythe distance from the plasma forming region P in whichhigh-concentration plasma is generated to the inner surface 54 a of theinner member 70 can be increased and wear of the inner surface 54 a ofthe inner member 70 can be reduce.

A cathode outer periphery recess portion 78 d is provided on the innersurface 54 a of the inner member 70. The cathode outer periphery recessportion 78 d is provided at a position facing the cathode 56 on theouter periphery of the inner member 70. The cathode outer peripheryrecess portion 78 d is configured to have a cylindrically curved surfacecorresponding to the cylindrical cathode 56. The cathode outer peripheryrecess portion 78 d is separated from the cathode 56 to secure theelectrical insulation between the cathode 56 and the slit member 54.

Inner engagement portions 78 p and 78 q are provided on the innersurface 54 a of the inner member 70. The inner engagement portions 78 pand 78 q engage with main body engagement portions which are provided onthe main body 52 of the arc chamber 50, thereby regulating the positionof the inner member 70 with respect to the main body 52. The innerengagement portions 78 p and 78 q are recess portions which are providedon the inner surface 54 a of the inner member 70, and the main bodyengagement portions protruding from the main body 52 are inserted intothe inner engagement portions 78 p and 78 q. A first inner engagementportion 78 p is provided in the vicinity of the cathode accommodationrecess portion 78 a, and a second inner engagement portion 78 q isprovided in the vicinity of the repeller accommodation recess portion 78b. The first inner engagement portion 78 p is formed such that a size inthe axial direction is substantially the same as a size in a horizontaldirection perpendicular to the axial direction. On the other hand, thesecond inner engagement portion 78 q is formed in a shape long in theaxial direction, and the size in the axial direction is larger than thesize in the horizontal direction. The shapes of the first innerengagement portion 78 p and the second inner engagement portion 78 q arenot limited to those shown in the drawing, and may be other shapes aslong as the position of the inner member 70 can be regulated byengagement with the main body engagement portions.

An inner member accommodation recess portion 84, a first outer peripheryrecess portion 88 a, and a second outer periphery recess portion 88 bare provided on the outer member 80. The inner member accommodationrecess portion 84 has a size corresponding to the external shape of theinner member 70 and accommodates the inner member 70. The first outerperiphery recess portion 88 a is provided at a position facing thecathode 56 on the outer periphery of the outer member 80 and isconfigured to have a cylindrically curved surface corresponding to thecylindrical cathode 56. The first outer periphery recess portion 88 a isseparated from the cathode 56 to secure the electrical insulationbetween the cathode 56 and the slit member 54. The second outerperiphery recess portion 88 b is provided at a position facing therepeller 58 on the outer periphery of the outer member 80. The secondouter periphery recess portion 88 b is configured to have the same shapeand size as the first outer periphery recess portion 88 a and isconfigured such that the outer member 80 has a vertically symmetricalshape. Therefore, the outer member 80 can be used upside down and canalso be mounted such that the first outer periphery recess portion 88 aand the repeller 58 face each other and the second outer peripheryrecess portion 88 b and the cathode 56 face each other. The second outerperiphery recess portion 88 b may not be provided on the outer member80. The repeller shaft 58 b which can face the second outer peripheryrecess portion 88 b has a smaller radial size (that is, is thinner) thanthat of the repeller head 58 a, and thus, even if the second outerperiphery recess portion 88 b is not provided, the electrical insulationbetween the repeller 58 and the slit member 54 can be sufficientlysecured.

FIG. 5 is a sectional view showing a schematic configuration of the arcchamber 50 and shows a cross section perpendicular to the axialdirection at the center 60 c of the front slit 60. FIG. 5 corresponds tothe cross section taken along the line C-C in FIG. 4 and shows a crosssection when the repeller 58 is viewed from the cathode 56. As shown inthe drawing, the repeller 58 is disposed so as to protrude outward fromthe front side 52 g of the main body 52, and a part of the repeller 58overlaps the slit member 54 in the axial direction. The cathode 56 isalso disposed, similar to the repeller 58, so as to protrude outwardfrom the front side 52 g of the main body 52, and a part of the cathode56 overlaps the slit member 54 in the axial direction. The protrusionportion 74 protrudes toward the outside of the arc chamber 50 around theinner opening 72, and the slit recess portion 76 is provided inside ofthe protrusion portion 74. The slit recess portion 76 is configured tobe separated from the cathode 56 and the repeller 58 in the radialdirection perpendicular to the axial direction so as not to overlap thecathode 56 and the repeller 58 in the axial direction.

FIG. 6 is a sectional view showing a schematic configuration of the arcchamber 50 and corresponds to the cross section taken along the line D-Din FIG. 4. FIG. 6 shows a cross section perpendicular to the axialdirection at a position corresponding to the cathode accommodationrecess portion 78 a and the first inner engagement portion 78 p. Asshown in the drawing, the cathode 56 is disposed so as to protrudeoutward from the front side 52 g of the main body 52, and a part of thecathode 56 is disposed inside of the cathode accommodation recessportion 78 a. Further, the main body 52 is provided with a first mainbody engagement portion 52 p protruding from the front side 52 g. Thefirst main body engagement portion 52 p engages with the correspondingfirst inner engagement portion 78 p to regulate the position of theinner member 70.

FIG. 7 is a sectional view showing a schematic configuration of the arcchamber 50 and corresponds to the cross section taken along line the E-Ein FIG. 4. FIG. 7 shows a cross section perpendicular to the axialdirection at a position corresponding to the repeller accommodationrecess portion 78 b and the second inner engagement portion 78 q. Asshown in the drawing, the repeller 58 is disposed so as to protrudeoutward from the front side 52 g of the main body 52, and a part of therepeller 58 is disposed inside of the repeller accommodation recessportion 78 b. Further, the main body 52 is provided with a second mainbody engagement portion 52 q protruding from the front side 52 g. Thesecond main body engagement portion 52 q engages with the correspondingsecond inner engagement portion 78 q to regulate the position of theinner member 70.

FIGS. 8 and 9 are side views schematically showing a method of fixingthe slit member 54. FIG. 8 shows a state where the slit member 54 isreleased from the main body 52, and FIG. 9 shows a state where the slitmember 54 is fixed to the main body 52. The arc chamber 50 is fixed to astructure 90. The structure 90 is provided with an accommodation recessportion 92 which accommodates and supports the main body 52, and lockingstructures 94 a and 94 b for fixing the slit member 54. The lockingstructures 94 a and 94 b engage with the outer engagement portions 86 aand 86 b provided on the outer member 80, and the slit member 54 isfixed to the main body 52 by applying a tensile force toward the mainbody 52 to the outer member 80. The first locking structure 94 aincludes a first rod 96 a having a tip portion which engages with thefirst outer engagement portion 86 a, a first bearing portion 97 a whichsupports the first rod 96 a, and a first spring 98 a for applying atensile force to the first rod 96 a. The first rod 96 a is configured tobe displaceable in a longitudinal direction and a directionperpendicular to the longitudinal direction with the first bearingportion 97 a as a support point, and is configured such that a disposedangle of the first rod 96 a is variable in a direction away from the arcchamber 50 and a direction approaching the arc chamber 50 at the time ofmounting and dismounting of the first rod 96 a.

The second locking structure 94 b is configured in the same manner asthe first locking structure 94 a and includes a second rod 96 b, asecond bearing portion 97 b, and a second spring 98 b. The secondlocking structure 94 b engages with the second outer engagement portion86 b to fix the slit member 54 with respect to the main body 52. Thestructure 90 is provided with a third locking structure and a fourthlocking structure (not shown). The third locking structure engages withthe third outer engagement portion 86 c shown in FIG. 3, and the fourthlocking structure engages with the fourth outer engagement portion 86 dshown in FIG. 3. The slit member 54 is pulled toward the main body 52 bythe four locking structures and is fixed with respect to the main body52. At this time, the first main body engagement portion 52 p and thefirst inner engagement portion 78 p engage with each other and thesecond main body engagement portion 52 q and the second inner engagementportion 78 q engage with each other, whereby the inner member 70 isaccurately positioned with respect to the main body 52.

Next, the operational effects which the ion generator 10 exhibits willbe described. According to this embodiment, the inner surface 54 a ofthe slit member 54 is made of graphite and the front slit 60 is definedby the inner opening 72 made of graphite, whereby mixing ofcontamination into the ion beam IB can be minimized. The inner surface54 a of the slit member 54 is a location which is exposed tohigh-concentration plasma in the plasma forming region P, and it can besaid that the inner surface 54 a is a location where the contribution ofmixing of contamination into the ion beam IB which is extracted from thefront slit 60 is the largest. By using graphite in such a location, itis possible to suitably suppress the mixing of contamination into theion beam IB, and in particular, the mixing of metal elements of therefractory metal material itself or trace amounts of metal elementscontained in the refractory metal material can be effectivelysuppressed.

According to this embodiment, the cathode head 56 b and the repellerhead 58 a are made of a refractory metal material, whereby it ispossible to reduce wear due to plasma as compared with a case wherethese members are made of graphite, and to reduce dirt that can bedeposited inside of the arc chamber 50. Further, by increasing thepurity of the refractory metal material configuring the cathode head 56b and the repeller head 58 a, it is possible to suitably suppress mixingof contamination into the plasma which is generated in the plasmaforming region P. Further, the inner surface 52 a of the main body 52which is not easily worn by plasma is made of a refractory metalmaterial having standard purity, whereby it is possible to suitablysuppress mixing of contamination into the plasma which is generated inthe plasma forming region P while suppressing an increase in cost due tohigh purification.

According to this embodiment, a cover that is the outer member 80 madeof a refractory metal material is mounted to the side of outer surface54 b of the slit member 54, whereby an electric discharge that can occurbetween the slit member 54 and the extraction electrode 11 can besuppressed and damage due to the electric discharge can also besuppressed. In particular, by reducing the exposed area of the outersurface 74 b of the protrusion portion 74 around the inner opening 72 asmuch as possible, it is possible to enhance the effect of suppressing anelectric discharge due to the graphite being exposed to the extractionelectrode 11 and as a result, it is also possible to enhance the effectof suppressing damage due to the electric discharge. Further, the edgeof the outer opening 82 of the outer member 80 is provided at a positionfarther from the center 60 c of the front slit 60 than the taperedsurface 72 a and the virtual plane 72 b of the inner opening 72, wherebymixing of contamination attributed to the outer member 80 into the ionbeam IB which is extracted from the front slit 60 can be suppressed.

According to this embodiment, the cathode accommodation recess portion78 a, the repeller accommodation recess portion 78 b, and the centerrecess portion 78 c are provided on the inner member 70, whereby thecathode 56 and the repeller 58 can be disposed closer to the slit member54 while increasing mechanical strength by increasing the thickness ofthe outer periphery of the inner member 70. As a result, the distancefrom the plasma forming region P interposed between the cathode 56 andthe repeller 58 to the front slit 60 can be shortened, and theextraction efficiency of multiply charged ions which are generated morein the vicinity of the center of the plasma forming region P can beincreased. In this way, more multiply charged ions can be supplied tothe downstream of the ion generator 10. Further, in conditions where thesupply amounts of multiply charged ions are approximately the same, byadopting the configuration of this embodiment, an arc voltage or an arccurrent can be relatively reduced, and thus wear of the arc chamber oran electric discharge between the arc chamber and the extractionelectrodes can be suppressed.

The present invention has been described above with reference to theembodiment. However, the present invention is not limited to theembodiment described above, and appropriate combinations or replacementsof the configurations of the embodiment are also included in the presentinvention. Further, it is also possible to appropriately rearrange thecombination or the processing order in the embodiment or to addmodifications such as various design changes to the embodiment, based onthe knowledge of those skilled in the art, and embodiments to which suchrearrangement or modifications are added can also be included in thescope of the present invention.

It should be understood that the invention is not limited to theabove-described embodiment, but may be modified into various forms onthe basis of the spirit of the invention. Additionally, themodifications are included in the scope of the invention.

What is claimed is:
 1. An ion generator comprising: an arc chamber whichdefines a plasma generation space; and a cathode which emitsthermoelectrons toward the plasma generation space, wherein the arcchamber includes a box-shaped main body which includes an opening in atleast part of a front side of the main body, and a slit member which ismounted to cover the opening of the front side of the main body andprovided with a front slit for extracting ions, an inner surface of themain body which is exposed to the plasma generation space is made of afirst refractory metal material, the slit member includes an innermember made of graphite, and an outer member made of a second refractorymetal material, the outer member includes an outer surface which isexposed to an outside of the arc chamber, and the inner member includesan inner surface which is exposed to the plasma generation space and anopening portion which forms the front slit extending from the innersurface of the inner member to the outer surface of the outer member. 2.The ion generator according to claim 1, wherein the outer member isprovided with an outer opening for forming the front slit, and anopening size of the outer opening is larger than an opening size of theinner opening.
 3. The ion generator according to claim 2, wherein theinner member includes a tapered surface which is provided at an edge ofthe inner opening such that an opening size increases from an insidetoward an outside of the arc chamber, and an edge of the outer openingis provided at a position farther from a center of the front slit than avirtual plane obtained by extending the tapered surface toward theoutside of the arc chamber.
 4. The ion generator according to claim 2,wherein the inner member includes a protrusion portion which protrudestoward the outside of the arc chamber on a periphery of the inneropening, and an edge of the outer opening is provided along an outerperiphery of the protrusion portion of the inner member.
 5. The iongenerator according to claim 4, wherein a position of an outer surfaceof the outer member on a periphery of the outer opening in a thicknessdirection from the inside toward the outside of the arc chambercoincides with a front surface of the protrusion portion of the innermember which is exposed to the outside of the arc chamber.
 6. An ionimplanter comprising: an ion generator that comprises an arc chamberwhich defines a plasma generation space, and a cathode which emitsthermoelectrons toward the plasma generation space, wherein the arcchamber includes a box-shaped main body which includes an opening in atleast part of a front side of the main body, and a slit member which ismounted to cover the opening of the front side of the main body andprovided with a front slit for extracting ions, an inner surface of themain body which is exposed to the plasma generation space is made of afirst refractory metal material, the slit member includes an innermember made of graphite, and an outer member made of a second refractorymetal material, the outer member includes an outer surface which isexposed to an outside of the arc chamber, and the inner member includesan inner surface which is exposed to the plasma generation space and anopening portion which forms the front slit extending from the innersurface of the inner member to the outer surface of the outer member. 7.The ion implanter according to claim 6, wherein the first refractorymetal material includes the same refractory metal element as the secondrefractory metal material.
 8. The ion implanter according to claim 6,wherein the inner opening portion includes an exposed portion which isexposed to the outside of the arc chamber, and the outer membersurrounds the exposed portion.
 9. The ion implanter according to claim8, wherein at least part of the outer member faces the inner member in athickness direction from the inside toward the outside of the arcchamber.
 10. An ion implanter comprising: a beam generation unit thatcomprises an ion generator to generate multiply charged ions, and thatgenerates an ion beam of the multiply charged ions extracted from theion generator; a beam acceleration unit that accelerates the ion beam toobtain a high energy ion beam of 1 MeV or more; and a substrateprocessing unit in which the high-energy ion beam is implanted into asubstrate, wherein the ion generator includes an arc chamber whichdefines a plasma generation space, and a cathode which emitsthermoelectrons toward the plasma generation space, the arc chamberincludes a box-shaped main body which includes an opening in at least apart of a front side of the main body, and a slit member which ismounted to cover the opening of the front side of the main body andprovided with a front slit for extracting ions, an inner surface of themain body which is exposed to the plasma generation space is made of arefractory metal material, and an inner surface of the slit member whichis exposed to the plasma generation space is made of graphite.
 11. Theion implanter according to claim 10, wherein the beam acceleration unitcomprises a linear accelerator.
 12. The ion implanter according to claim10, wherein the beam acceleration unit comprises a plurality of linearaccelerators.
 13. The ion implanter according to claim 10, wherein thebeam acceleration unit accelerates the ion beam to obtain a high energyion beam of 4 MeV or more.
 14. The ion implanter according to claim 10,wherein the ion generator generates the multiply charged ions of atleast one of boron, phosphorus, and arsenic.